Date:         Sun, 30 Jul 2000 09:29:08 -0700
Reply-To:     Stanley Pitman <stanman@blueneptune.com>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Stanley Pitman <stanman@blueneptune.com>
Subject:      Auxiliary batteries revisited (and goodbye)
Content-Type: text/plain; charset="us-ascii"

Some of you might remember my postings from several weeks ago, sharing my
engineering knowledge about battery isolators, relays and other such
matters.  In the interim, I have done some more digging to round out my
battery education.

To summarize:

Ordinary deep-cycle RV or marine batteries are made for relatively slow
charging or discharging.  High charging rates will cause battery damage
over time.  Charging at high rates requires special batteries, such as the
Optima units recommended by several folks' postings.  They are expensive
but durable.

How fast should you charge the auxiliary battery ?.  This should ideally be
determined by your usage and needs, rather than being set by whatever
charging widget you've gotten at a bargain price.  Widgets can be fine as
long as you understand and can adapt to their limitations.

If you typically lightly deplete your battery while camping, and then drive
an hour or so before you camp again, you may get by with a low charge-rate
widget like some of the small relay kits on the market. The charging
current is typically limited by the size of the wire and relay used, and by
the fuse that protects both wires and relay contacts from frying.

If you regularly drain your battery way down, on the other hand, your
widget might need driving all day for full recharging.   Heavy relays and
their associated heavier wiring can give much faster charging, but
selecting the right relay, wire and fuse can be a bit complicated.

Fast recharging of deeply discharged auxiliary batteries plus an aging
starter battery can put a heavy load on an alternator, especially a 65 amp
unit.  90 amp units are marginally better, at least when in good shape.  To
avoid overloading alternators right after restarting an engine, battery
separators and combiners, sold by Sure Power and West Marine, hold off
connecting auxiliary charging until the starter battery is at least
partially recharged.

Battery  isolators can also allow high rate auxiliary charging, by
splitting the charging current between two batteries according to their
needs.  In Vanagons, it should ONLY be done using a special isolator and by
making modifications to your alternator, as detailed by Harald's postings.
 Do NOT try to use bargain basement isolators not meant for Bosch alternators.

That about wraps it up for me.  Although it's been an interesting and
educational ride, I must bid adieu to the list group and to my beloved '86
Syncro, which always wanted to grow up to be a Dodge Power Wagon.  It now
has a new home with another list member.

My special thanks to Harald Rust, Beckett Cantrell and a few others for
furthering my knowledge and providing some chuckles in the process.  I'm
going to miss their sage counsel.

Stanley Pitman